You have a couple of options...
If you have room for some lumber, you can bring a couple of 2x8's and use them as step-ramps. That will decrease the angle coming onto the trailer.
If you don't want to go that route, jack the front of the trailer as high as you can, which should lower the rear and the ramps to decrease the angle. Make sure you keep the trailer secured to the ball on the tow vehicle if you do this - otherwise you are going to be repairing a bunch of things... been there, seen that...
The other thing to watch, and I've never used a U-haul, is will the door clear the trailer fender? If not, you're gonna have fun getting out of the car or closing the window. Again, you can always use some lumber under the drivers side tires to tilt the car slightly and clear the fender.
On my enclosed trailer, I have 2x10 blocks screwed into the floor where the drivers side tires should stop. That picks that side of the car up just enough that I can open the door through the escape door in the side of the trailer.